A year of rusty patched bumble bee observations - still hope for the species

Rusty patched bumble bee. Photo by USFWS.

By Andrew Horton
Minnesota-Wisconsin Ecological Services Office

After a year of new observations for the rusty patched bumble bee, the core range of the species continues to grow. Since this species was listed as endangered in the spring of 2017, we have made new observations, primarily in southwest Minnesota, southern Wisconsin and northern Illinois. New populations have also been discovered in Iowa and Virginia.

The number of individual bees sighted is also up from previous years. The higher number of observations is likely a factor of increased survey effort and awareness, but could also be a sign of a good production year for the bumble bee colonies. In 2016, a total of 48 individual bees were reported across the entire range of the species. In 2017 the number of individual bees sighted increased to 191 across 102 sites; many observations were of a single bee observed in a particular location.

So far in 2018, there have been more than 300 individual rusty patched bumble bees reported, and many locations are documenting four to 12 individuals observed at a time. This could be an indicator of a healthier local colony that is producing more worker bees than in past years, or that the observation point may be closer to the colony. Rusty patched bumble bee colony nests are thought to be located underground, such as in abandoned rodent burrows.

The rusty patched bumble bee has declined by 87 percent in the last 20 years. The species is likely to be present in only 0.1 percent of its historical range. There are many potential reasons for the rusty patched bumble bee decline including habitat loss, intensive farming, disease, pesticide use and climate change.